Production of metal powder



March 4, 1952 H. A. GOLWYNNE PRODUCTION OF'METAL POWDER Filedsept. 29, 1949 M') FILTER V COMPRESSOR/ mm om A l m /M N u W en.. m

ATTORNEYS Patented Mar. 4, 1952 UNITEDl STATES PRODUCTION F METAL POWDER Henry A. Golwynne, New York, N. Y.

Application September 29, 1949, Serial No. 118,623

19vClaims.

l This invention relates* to the production of metal powder and has for its object certain improvements inthe method of and-,apparatus for producing metalv powders, Various proposalsl have'been advanced for producing metal powder in an inert or non-reactive atmosphere. To thisend a body ofmolten metal isY converted intovery iinely divided particles and the'particles are then frozen into powder with the gas. The body-ofmolten metal may beY converted into nely divided particles in various Ways, such as by spraying; vaporization, atomizaticn, etc. In my copending applications, Ser; Nos. 118,621 and 118,622, filed September 29, 1949, simultaneouslyherewith@ I have described and claimed an improvedv method and apparatus for conducting thev operation` by atomization of .molten metal with a blast of inert gas, freezing the atomized metal into finely divided particles and recovering the resulting metal powder- In accordance with thev method, theA molten metal atomizing, metalf powder forming and powder separating, steps are conducted in a confined circulatory system lled with inert gas continuously circulating therethroughr under a pressure higher than atmospheric to prevent ingress of outside air. And, in accordance with the apparatus, the improvement comprises a conned circulatory system adapted to be' filled withl gas-under pressure higher than atmospheric, the system `inl cluding a gasometerv to hold surplus gas and to take careY of expansion and contraction of the gas, a chamber for atomizing molten metal and ,chilling` atomized molten,4 metal into powder, a

blower for circulating the gas-around the system,

and a separator for separating the powder from the gas.

Most metals havea marked aiiinity for oxygen and nitrogenA atl elevated temperaturesl and most -.socalled inert gases contain oxygen and nitrogen. This makes it diiiicult toproduce metal powder from nely divided particles of molten metal-in such a gas. Oxides and nitrides formed by the reaction of oxygen and nitrogen in the gas with the finely divided particles of metal tend to form at or near and to contact and then to adhere to the highly heated device usedI to spray, vaporize or atomize the moltenv metal, thus clogging orotherwise impairing its usefulness.

Inert gases available commercially in quantities n at `relatively lowcost arenot truly inert and even if truly inert other oxidizing and nitridingI inuences are inherent in the operation. Investigators in thisv iieldV have. been,l greatly troubled with the problemof getting sumcientlr inert or non-reactive atmospheres in which to conduct the operation. As manufactured thegas itself., for example, helium, argon, etc., is not entirely inert-because it usually contains a certain amount of such impurities as oxygen and nitrogen. The inert gas must be conducted into a` chamber in which the molten metal is to be converted. into the finely divided particles and chilled into powder form. Since the chamber is initially filled with air,vthe air must be ushed out or otherwise be replaced by the inert gas. In spite of special precautions a residuum of air remains, and since the air is rich in oxygen and nitrogen, the at-4 mosphere as a whole in the chamber is contaminated to that extent. The finely divided molten metal particles react readily withthe oxygen and nitrogen. Oxide and nitrideincrustations then form on the device used to produce the finely divided particles of molten metal, thereby impairing its usefulness.v The operation must then be stopped to clean or replace the device.

As a result of my investigations, I .have discovered that diiicultiesand disadvantages ofthe kind mentioned may for the most DartV be overcome. Certain, improvements in the method of and apparatus for producing the metal powder may be so utilizedcas to avoid the harmfuleffects of such impurities as oxygen and nitrogen.

In accordancewithv the method ofV the invention a. conned circulatory system, including metal forming and powder-separating zones, is lled with inert gas under pressure higher than atmospheric to prevent ingress. of outside air. The gas in the system is puried with respect to such impurities as oxygenand nitrogen, The desired metal powder is then produced in the presence of. the gas sov puried, as it is circulated through the system. In a presently preferred practice, the oxygen and nitrogen, impurities are madeY to react with a body of finely divided particles of heated metal to form the oxide and. nitride of themetal.-

Air initially present in theV circulatory system is replaced for the most part with the inert` gas andf the oxygen and nitrogen in the residuek of air remaining in the inert gas are made tofreact withY the heated metal particles. To this end someof the` inert gas is by-passed from the system,` asthe main body of inert gas circulates throughthe system. The by-passed inert gas is purified with respect to the oxygen and nitrogen, and, the purified inert gas is then returned to the system. Thiscyclic operation is continued, until all of thefinert gas in the system reaches the desired purity f above inlet 2i?.

In accordance with the apparatus of the invention, the improvement comprises a confined circulatory system adapted to be lled with the incrt gas under pressure higher than atmospheric to prevent ingress of outside air. The system includes a powder forming chamber and a purifier for the gas, the purifier being adapted to remove such impurities as oxygen and nitrogen from the gas. In a preferred practice, the purifier is provided with a perforated container adapted to hold a body of the finely divided metal particles through which the gas may be passed as the oxygen and nitrogen react with the metal to form an oxide and nitride. Means are provided for heating the metal particles to a temperature sufficiently high for the reactions to take place.

A compressor is advantageously included in the system. The inlet or suction side of the compressor connects with the system so that gas may be withdrawn therefrom. 'Ihe outlet or pressure side of the compressor connects with the inlet of the purifier while the outlet of the purifier connects with the system so that purified gas may be returned thereto. The purifier preferably is provided with a plurality of the perforated containers to hold a plurality of bodies of the finely divided metal particles. In a present practice the purifier is in the form of an upright imperforate chamber provided with superposed perforated containers adapted to hold layers of the finely divided metal particles.

These and other features of the invention will be better understood by referring to the accompanying drawings, taken in conjunction with the following description, in which:

Fig. 1 is a diagrammatic side elevation of an apparatus illustrative of a practice of the invention, showing the manner in which a compressor and a purifier may be hooked-up;

Fig. 2 is a side elevation partly in section of the purifier;

Fig. 3 is a plan view of one ofthe trays or baskets in the purifier; and

Fig. 4 is a section on the line Q of Fig. 3.

Referring first to Fig. 1, the apparatus shown includes a compressor ID with an inlet conduit I2 on its inlet or suction side, which in turn connects with the circulatory system (not shown), such as described in my copending applications.

An outlet conduit M connects the outlet or pressure side of the compressor with a filter I6. The filter is adapted to remove such impurities as dust. moisture and oil, if present in the gas to be purified. Another outlet conduit I8 connects the lter with an inlet conduit 2i) leading into the bottom portion of a purifier 22. An outlet conduit 24 connects the upper end of the purifier with the main circulatory system (not shown). Outlet conduit i8 also connects with the melting furnace and atomizer (not shown), such as de scribed in the copending applications. A heating chamber 25 surrounds the purifier and is provided with an inlet 2B for heating gases and an outlet 3!! for the escape of spent heating gases.

Fig. 2 shows the interior construction of the purifier. It is cylindrical in form with a closed bottom 32 resting on supports 34 on the bottom of the interior of the heating chamber. Superposed trays or baskets se rest on an inner fiange support 38 integrally secured to the side wall of the purifier, the flange being located'directly An imperforate cover 40 is securable to the top of the purifier by means of 'a plurality of bolts 42 through the outer flange M. All joints of.' the purifier are gas tight so that heating chamber gases cannot .enter the purifier and so that gases inside the purifier cannot escape into the heating chamber.

The trays are generally cylindrical in shape, being formed of a band of sheet metal 46 with a turned in bottom flange 48 and a similar turned in top flange 5U. A circular piece of coa-rse mesh screen 52 rests on and is secured to the bottom ange. A circular piece of fine mesh screen 54 in turn rests on the coarse mesh screen, the latter serving as a strong support for the former. A relatively thin layer of finely divided metal particles 55, such as magnesium powder, if magnesium powder is to be produced, rests on the screen. A handle or bar '58 is secured to the underside of upper flange 50.

In preparing the purifier for use, cover 40 is removed and the loaded trays or baskets are placed therein, one superposed on the other. In the case of the bottom tray, its bottom flange 48 will rest on inner fiange support 38. Lower flange 48 of the second tray will rest on upper flange 50 of the first tray, etc. The purifier is provided with a sunicient number of the loaded trays. Cover 4i) is then returned and bolted securely.

The apparatus may be operated as follows: Heating gases are passed through inlet 28 into heating chamber 2B where they surround and heat purifier 22. Trays 36 and their layers 56 of metal particles are thus indirectly heated. The gas to be purified is drawn by suction from the circulatory system through inlet l2 into compressor IB and passed through outlet I4, filter I5, outlet I8 and inlet 2D into the bottom portion of the purifier. The gas, being under sufficient pressure by the compressor, then rises upwardly through the trays where it comes into intimate and repeated contact with the metal particles in the layers resting on the screen bottoms of the trays. The heating gases supplied to the heating chamber are suiciently hot to raise the temperature of the metal particles to a point Where the oxygen and nitrogen in the gas to be purified react therewith to form metal oxide and metal nitride. Spent heating gases rise to the top of the heating chamber and escape through outlet 30 into the open atmosphere. The puriiied gas, however, leaves the purier at its top through outlet 24and is returned to the main circulatory system.

The operation is a continuous or cyclic one until all of the gas in the circulatory system is passed repeatedly through the compressor and the purifier. When tests, with an O-rset tester, of the gas show that the oxygen has been removed, the purifier circuit may be closed. With the main system filled with purified inert gas. the production of lmetal powder may proceed. If the gas in the system should become impure with respect to oxygen and nitrogen, such as by inadvertent leaks ofoutside air into the system, or by the additions of impure inert gas to the system, or both, the purification circuit may again be opened and the gases be further purified. The production of metal powder may proceedsimultaneously with the purification operation but in general it is better first to purify the gas and then to produce metal powder.

It is advisable to have a purifier amply large, including trays and layers of metal particles, to purify all of the gas in the circulatory system. Once the main system is filled with inert gas, the metal powder production operation may be conducted over a relatively long period. Withv the o o nrayf'berremoved,I emptied' of' their metal oxide and nitride andfun-used'* metal, re-loaded with layers ofl metall particles and'A returned' for the next purification operation.

The molteny metalor alloy'to befconverted into powder vvis first subdividedintoa myriad offiinely dividedparticles, such as by spraying, vaporization or by atomizatiom in the presence" of the purified gas circulatin'gfin a powder forming zone. The newly formed'powder particles are then separated from thegas and recovered.

While th'epurication system may be used in the production of various metal'and metal alloy powders, it is now being used for the production of'magnesium powder and magnesium-aluminum alloy powders. Since some powder of the kind to be produced is usually atY hand, the layersl of metal particles in the trays are preferably formed from that'pow'der;

It is obvious to one skilled in this art that various modificationsv in method and apparatus are feasible in the practice of. the invention. The above is only by way of illustration, but it shows how effectively it may be employed to purify gas in such a circulatory system.

I claim:

1f. In the method of producing metal powder by` atomizing a body of molten metal into very.

finely divided particles and freezing the particles into powderwith a gassubstantially inert to the metal, the main body of gas being coniined in a main circulatory system under pressure higher than atmospheric to prevent ingress of outside air, the improvement which comprises withdrawing gas` from the main circulatory system when contaminated with an objectionable amount of such impurities as oxygen and nitrogen, purifying the gas withdrawn with respect to the oxygen and nitrogen, and returning the puried gas to the main circulatory system.

2. Method according to claim 1, in which the oxygen and nitrogen impurities in the gas are made to react with a heated body of finely divided metalv particles to form an oxide and nitride of the metal. "s

3. Method according to claim l, in which the gas withdrawn from the main circulatory system is elevated in pressure in advance of the puriiication step.

4. Method according to claim 1, in which the gas withdrawn from the main circulatory system is compressed to increase its pressure, and the compressed gas is forced through a heated body of nely divided metal particles so that the oxygen and nitrogen impurities may react therewith to form an oxide and nitride of the metal.

5. Method according to claim 1, in which the -operation is continued until all of the gas in the main circulatory system reaches the desired purity.

6. Method according to claim 1, in which the gas withdrawn from the main circulatory system is compressed to increase its pressure, the compressed gas is forced through a body of heated metal particles so that the oxygen and nitrogen impurities may react therewith to form an oxide and nitride of the metal, and the operation is continued until all of the gas in the main circulatory system reaches the desired purity 7. Method according to claim 1, in which the gas withdrawn from the main circulatory system is compressed to elevate its pressure, the compressed gas is forced through a filter to remove metal powder therefrom, and the ltered gas is forced through a heated body of finely divided 6, metal particles so that the oxygen and nitrogen impurities may react therewith to forman oxide and nitride of the metal.

8. Method accordingfto claim 1, in which the gaswithdrawn from the main circulatory system is compressed to elevate its pressure, and the compressed gas is forced through a plurality of heated bodies of finely divided metal so that the oxygen and nitrogen impurities may reacttherewith to form an oxide and nitride of the metal.

9i Apparatus for producing metal powder by atomizing a body-of molten metal into very finely divided particles and freezing the particles into powder 'with a gas substantially inert to the metal, the main body of gas beingV confined in a main circulatory system under pressure higher than atmospheric to prevent ingress of outside air,- the improvement comprising a purifier for removing such impurities as oxygen and nitrogen from the gas to render. it practicallyinert to the metal, a by-pass conduit connecting the main circulatory system with the inlet of the purifier forl the withdrawal of gas from the main circulatory system and lits passage through the purifier, and a conduit connecting the outlet of the purifier with the main circulatory system for returning gas so purified to the main circulatory system. f

10. Apparatus according to claim 9, in which `the purifier is provided with a perforated container for holding a heated body of finely divided metal particles through which the gas may be passed so that the oxygen and nitrogen impurities may react with the metal particles to form an oxide and nitride thereof.

11. Apparatus according toclaim 9, in which the purifier is provided with a perforated container for holding a heated body of finely divided metal particles through which the gas may be passed so that the oxygen and nitrogen impurities may react with the metal particles to form an oxide and nitride thereof, and means are provided for heating the body of metal particles to a temperature sufciently high for the reactions to take place.

12. Apparatus according to claim 9, in which the purifier is in the form of an imperforate chamber fitted with a plurality of removable perforated containers for holding heated bodies of nely divided metal particles through which the gas may be passed, and means for heating the metal particles in the containers in the chamber.

13. Apparatus according to claim 9, in which the purier is in the form of an upright imperforate chamber provided with a plurality of superposed removable perforated containers for holding heated bodies of metal particles through which the gas may be passed so that the oxygen and nitrogen impurities may react with the metal particles to form an oxide and nitride thereof, and means for heating the metal particles,l in the containers in the chamber.

14. Apparatus for producing metal powder by atomizing a body of molten metal into very finely divided particles and freezing the particles into powder with a gas substantially inert to the metal, the main body of gas being confined in a main circulatory system under pressure higher than atmospheric to prevent ingress of outside air, the improvement comprising a compressor for increasing the pressure of the gas, a bypass conduit connecting the main circulatory system with the inlet of the compressor for the withdrawal of gas from the main circulatory system and its passage through the compressor, a purifier for removing such impurities as oxygen and nitrogen from the gas, a conduit connecting the outlet of the compressor with the inlet of the purifier for the passage of the compressed gas through the purifier, and a conduit connecting the outlet of the purifier with the main circulatory system for returning gas so puried to the main circulatory system.

15. Apparatus according to claim 14, in Which the purier is provided with a perforated container for holding a heated body of finely divided metal particles through which the gas may be passed so that the oxygen and nitrogen impurities may react with the metal particles to form an oxide and nitride thereof.

16. Apparatus according to claim 15, in which the purifier is provided with a perforated container for holding a heated body of finely divided metal particles through which the gas may be passed so that the oxygen and nitrogen impurities may react with the metal particles to form an oxide and nitride thereof, and means are provided for heating the body of metal particles to a temperature sufciently high for the reactions to take place.

1'7. Apparatus according to claim 14, in which the puriiier is in the form of an imperforate chamber tted with a plurality of removable perforated containers for holding heated bodies of land means for heating finely divided metal particles through which the 18. Apparatus according to claim 14, in which the purifier is in the form of an upright imperforate chamber provided with a plurality of Superposed removable perforated containers for holding heated bodies of metal particles through Which the gas may be passed so that the oxygen and nitrogen impurities may react with the metal particles to form an oxide and nitride thereof, the metal particles in the containers in the chamber.

19. Apparatus according to claim 14, in which a lter is disposed in the conduit connecting the outlet of the compressor With theainlet of the purifier.

HENRY A. GOLWYNNE.

REFERENCES CITED ,The following references are of record in the nie of this patent:

UNETED STATES PATENTS Number Name Date 1,614,566 Marx Jan. 18, 1927 1,869,025 Seastone July 26, 1932 2,402,441 Paddle June 18, 1946 2,450,081 Burkhardt Sept. 28, 1948 

9. APPARATUS FOR PRODUCING METAL POWDER BY ATOMIZING A BODY OF MOLTEN METAL INTO VERY FINELY DIVIDED PARTICLES AND FREEZING THE PARTICLES INTO POWDER WITH A GAS SUBSTANTIALLY INERT TO THE METAL, THE MAIN BODY OF GAS BEING CONFINED IN A MAIN CIRCULATORY SYSTEM UNDER PRESSURE HIGHER THAN ATMOSPHERIC TO PREVENT INGRESS OF OUTSIDE AIR,THE IMPROVEMENT COMPRISING A PURIFIER FOR REMOVING SUCH IMPURITIES AS OXYGEN AND NITROGEN FROM THE GAS TO RENDER IT PRACTICALLY INERT TO THE METAL, A BY-PASS CONDUIT CONNECTING THE MAIN CIRCULATORY SYSTEM WITH THE INLET OF THE PURIFIER FOR THE WITHDRAWAL OF GAS FROM THE MAIN CIRCULATORY SYSTEM AND ITS PASSAGE THROUGH THE PURIFIER, AND A CONDUIT CONNECTING THE OUTLET OF THE PURIFIER WITH THE MAIN CIRCULATORY SYSTEM FOR RETURNING GAS SO PURIFIED TO THE MAIN CIRCULATORY SYSTEM. 